Ferrous alloys of exceptionally high strength



United States Patent Delaware No Drawing. Filed May 20, 1965, Ser. No.457,494 32 Claims. (Cl. 75123) The present invention relates to ferrousalloys and, more particularly, to ferrous-base alloys characterized bystrength levels of a tremendously high order of magnitude, to wit,tensile strengths above about 300,000 pounds per square inch (p.s.i.) toabout 500,000 p.s.i. and higher. Of considerable significance, theexceedingly high strengths manifested by alloys contemplated herein areobtained with the simplest of heat treatment. Recourse to costly and/orcomplicated processing techniques, including quenching, tempering,severe plastic deformation, e.g., ausforming, cold rolling, colddrawing, etc., is not at all necessary.

As is generally known to those skilled in steel metallurgy, importantand rather striking advances have been achieved within the last score ofyears in improving the strength capability of steel. A number of diversefactors have undoubtedly underscored this endeavor but infrequent hasbeen the case where the competitive necessity of developing steelshaving higher strength-to-weight ratios has not assumed an important, ifnot major, role. Such was the case in the development of steels havingyield strengths up to 100,000 p.s.i. as indicated in Metals Handbook,8th ed. (1960), p. 87, and also in the development of 200,000 p.s.i. to300,000 p.s.i. ultimate tensile strength steels.

Notwithstanding that steels of ultimate tensile strengths of up to about300,000 p.s.i. have become a commercial reality, research eflorts havebeen intensified in the quest of stronger and, thus, lighter steels(based on strength-to-weight ratios). Extremely versatile steels withyield strength of up to about 300,000 p.s.i. (yield strength ascontrasted with ultimate tensile strength being a basic tool of thedesigner) have recently been attained with a good level of toughness, amechanical property all too frequently found lacking at the higheststrength levels in respect of the so-termed ultra strong quenched andtempered low alloy steels. While various proposals have receivedprominence, among the most notable are the recently introduced maragingsteels and those steels amenable to the ausforming technique.

The aforementioned maraging steels, described in US Patents Nos.3,093,518 and 3,093,519, have been considered as having a combination ofcharacteristics, including strength and toughness, superior to any steeltheretofore known, particularly when compared with steels which did notrequire work hardening through plastic deformation to develop a highplateau of strength. For example, at the high yield strength level ofabout 300,000 p.s.i., tensile elongations of about 7% or 8% have beenreached together with reductions in area of about 30% or 35% (barproperties) in the maraging steels. Apart from strength and toughnessconsiderations, the maraging steels have been deemed particularlyattractive since a quenching operation is not required and, thus, thewell documented problems, e.g., distortion, warpage, dimensional change,etc., attendant the high strength, quenched and tempered,carbon-containing, low alloy steels were obviated. In addition, temperembrittlement problems characteristic of the latter steels were alsogreatly minimized, if not completely eliminated. Such attributes of themaraging steels undoubtedly attest to their rather spontaneouscommercial acceptance. However, due regard being given to the manyvirtues of known maraging steels, we are unaware of any such maragingsteel which manifests the capability of providing yield strengths of,say, 400,000 p.s.i. or 450,000 p.s.i.

Relatively high yield strength levels have been reported regardingsteels subjected to the application of the ausforming process whereincertain steels (usually, if indeed not always, of high carbon content)are heavily plastically deformed during a heat treating cycle and whilein the austenitic condition, whereby the strength of the steel isincreased and other properties may be improved. Upon completion of theplastic deformation operation, the steel is quenched and tempered. Inrespect of one particular steel of which we are aware, the literatureindicates that a yield strength of slightly over 400,000 p.s.i. wasobtained but this required an inordinately high degree of plasticdeformation, to Wit, over and the utilization of a narrow and criticaltemperature range. When nominally plastically deformed about 20% to 30%,comparatively little benefit is obtained. While the ausforming techniqueis indeed a significant achievement, the applicability thereof is, atpresent, quite restricted. The amount of working to achieve highstrengths is extremely high, e.g., over 70%, and this considerationapart from other disadvantageous factors tends to limit the size, shapeand form of products that can be produced. In addition, highcarbon-containing alloys are generally necessary to provide a desiredresponse to ausforming and were ausformed material welded, the hot-coldWork function of ausforming would, as a practical matter, be completelylost. Of further importance is the fact that the process in and ofitself is, at best, tedious and costly to carry out because of the verycareful operational control that must be exercised.

In accordance with the present invention, tensile strengths well above300,000 p.s.i. and up to about 500,- 000 p.s.i. not only can be obtainedbut are achieved with the processing advantages attendant the maragingsteels and without the disadvantages of the quenched and tempered orausformed steels. This is not to say, however, that the presentinvention is to be construed as excluding the application of anyappropriate processing or treating operation, e.g., plastic deformation.Cold working, for example, can be used to advantage; in fact, tensilestrengths above 500,000 p.s.i. have been obtained in accordance herewithby cold reducing but a nominal amount, to wit, 20% to 30%. It is perhapsof some interest to note that plastically deforming by 30% is quite farremoved from the percentage of plastic deformation reported inconnection with the ausforming process wherein highest strength levelshave been attained.

The magnitude of improvement in tensile strength (including yieldstrength) or strength plus ductility as contemplated herein can beillustrated by comparison with known maraging steels. From theconsideration of tensile strength only, alloys within the inventionboost the strength levels of prior art maraging steels by upwards of175,000 p.s.i. as to strength plus ductility and using correspondingperiods of development, if, for example, a maraging steel affording ayield strength level of about 300,000 p.s.i. is used as a representativestandard, the present invention encompasses alloys which boost the yieldstrength by a factor of at least about 75,000 p.s.i. to over 100,000p.s.i. with a concomitant increase in tensile ductility of from 50% toAgain, however, as will be appreciated by those skilled in the art, thepresent invention is not intended to be restricted to steels having ahigh degree of ductility. There are numerous commercial applicationswhere high strength or, for that matter, extreme hardness is of primesignificance and a high degree of ductility is not of major importance,e.g., dies, bearings, machine tools, knives, razor blades, etc.

It has now been discovered that exceedingly high ma,,- nitudes oftensile strengths (both yield and ultimate tensile strengths) andtremendously high strength-toweight ratios can be achieved with ferrousalloys containing certain essential constituents, notably, nickel,molybdenum and cobalt, provided that the constituents are correlated inrespect of each other and are maintained within special compositionalranges. As will become clearer "herein, the ferrous metallurgist,producer, designer, etc., will also have at his disposal steels whichwill fulfill the requirements of various specific applications. Wheretensile strengths above, for example, about 425,000 p.s.i. andadvantageously above about 450,000 p.s.i., and/or high hardness, e.g.,Rockwell C (R 60 or 62 or even 65 and above, are of primary importance,certain compositions will provide these properties. Where high strengthson the order of 400,000 p.s.i., e.g., 375,000 to about 425,000 p.s.i.and advantageously up to 450,000 p.s.i., are required together with agood level of ductility, this need is also satisfied in accordanceherewith. Higher levels of ductility can be obtained where magnitudes ofstrength of about 350,000 to 375,000 p.s.i. are satisfactory.

Accordingly, it is an object of the invention to provide a novel ferrousalloy.

It is another object of the present invention to provide a ferrous-basecomposition having what is believed to be (apart from whiskers,crystals, thin films, very thin wires and the like) the higheststrength-to-Weight ratio and highest strength heretofore reached in asteel not subjected to deformation (beyond, of course, the usual hotworking processing).

It is a further object of the invention to provide steels havingstrengths above 300,000 p.s.i., e.g., 350,000 p.s.i. and up to about500,000 p.s.i. and above.

Another object of the invention is to provide ferrous alloys whichmanifest exceptionally high strength, e.g., 400,000 to 425,000 or450,000 p.s.i., and which are duetile at such strength levels.

The invention further contemplates providing ferrous alloys which areextremely hard.

Other objects and advantages will become apparent from the followingdescription.

Generally speaking, the present invention contemplates ferrous alloyscontaining, by weight, from 5% to 16.5% nickel, e.g., 7% to nickel,about 7% to 16% molybdenum, e.g., 8% to 15% molybdenum, about 8% to 30%cobalt, e.g., 10% to 25% cobalt, the sum of the molybdenum plus cobaltbeing at least about 20% and advantageously at least about 22%, up to2.5% titanium, up to 2.5 aluminum with the sum of the titanium plusaluminum not exceeding about 3%, and advantageously not exceeding 2.5%,up to 0.3% carbon, the balance of the alloys being essentially iron. Aswill be readily understood by those skilled in the art, the term balanceor balance essentially when used in referring to the amount of iron inthe alloys does not exclude the presence of other elements commonlypresent as incidental elements, e.g., deoxidizing and cleansingelements, and impurities ordinarily associated therewith in smallamounts which do not materially affect the basic characteristics of thealloys. In this connection, elements such as sulfur, phosphorus,hydrogen, oxygen, nitrogen and the like should be maintained at lowlevels consistent with commercial practice. However, supplementaryelements can be present in the alloys as follows: up to 2% columbium,e.g., up to 1.5%; up to 4% tantalum, e.g., up to 3%; up to 0.1% boron,e.g., up to 0.05%; up to 0.25% zirconium, e.g., up to 0.15%; up to 8%chromium, e.g., up to 5%; up to 2% vanadium, e.g., up to 1.5%; up to0.5% silicon and advantageously not more than 0.25%; up to 0.5%manganese and advantageously not more than 0.25%; up to 0.1% calcium,e.g., up to 0.075%; up to 1% beryllium, e.g., up to 0.5%; and up to 4%copper, e.g., up to 2%. It is preferred that the respective amounts ofthe aforementioned supplementary elements be as follows: up to 1%columbium, e.g., 0.01% to 0.5%; up to 2% tantalum, e.g., 0.01% to 0.5%;up to 0.01% boron, e.g., 0.0005% to 0.0075%; up to 01% zirconium, e.g.,0.001% to 0.1%; up to 4% chromium, e.g., 0.1% to 3.5%; up to 1%vanadium, e.g., 0.1% to 0.5%; up to 0.15% silicon, e.g., 0.01% to 01%;up to 0.15% manganese, e.g., 0.01% to 0.1%; up to 0.05% calcium, up to0.1% beryllium, and up to 1% copper. The total sum of the supplementaryelements should not exceed 10% and advantageously should not exceed 6%.Tungsten can be used to replace molybdenum in part on an atom for atombasis, two parts of tungsten by weight for one part of molybdenum, in anamount up to 8% by weight. However, it is advantageous that the tungstennot exceed 6% and preferably should not exceed 4% particularly sincemolybdenum, in contrast to tungsten, importantly contributes to improvedforgeability and/or hot workability and also imparts enhanced ductilitycharacteristics.

Although a very substantial number of alloys have been prepared andsubjected to desired testing, the exact or complete metallurgicalexplanation regarding the behavior of the steels and the role of theirrespective constituents is not yet at hand. The behavior of the subjectsteels is deemed unusual indeed since while they can be considered asmaraging steels they run contra to certain accepted principles of knownmaraging steels. In any event and as will be demonstrated hereinafter,it has been found that it does not take much departure from thecompositional ranges set forth herein to lose the advantages of theinvention.

The element nickel contributes, among other things, to achievingductility, toughness and a desired martensitic structure upon coolingfrom hot working or, where used, solution treatment. The subject alloysare austenitic at high temperature and undergo transformation duringcooling. However, with excessive amounts of nickel, retained austenitein deleterious amounts can ensue and/ or there is danger of excessiveaustenite reversion upon aging. Austenite reversion can be minimized byusing low aging temperatures, e.g., below 700 F., but this, in turn,would significantly impair the strength level of the steels. Further,for a given molybdenum and cobalt content, it is considered that amaximum combination of strength and toughness is attained when thenickel content is at a level as high as is consistent with providing thelowest M temperature together with freedom of substantial amounts ofaustenite, e.g., amounts of austenite on the order of above about 5%.Other factors being equal, it is thought that with the low Mtemperatures a greater number of dislocation tangles are formed and, asa result thereof, strength characteristics are enhanced. Further, lownickel contents invite the tendency for formation of ferrite or otherundesirable and subversive phases and such phases can wreak havoc withvarious mechanical characteristics of the steels. Accordingly, it isadvantageous that the nickel content be from 7% to 16.5% and whereoptimum toughness characteristics are desired, it is most preferred thatthe nickel content be at least 11%, e.g., 11% to 16%.

Molybdenum and cobalt principally confer strengthening and hardeningcharacteristics, the former being the more potent in this regard.Molybdenum, as mentioned above herein, also provides, at high strengthlevels, good forgeability and ductility characteristics. The combinedamounts of molybdenum and cobalt should be at least 20% and for bestresults the total content of these elements should be at least 22% andpreferably at least 23%. Apart from the strengthening and hardnesscharacteristics imparted to the alloys by cobalt, it can be used in somemeasure in controlling the occurrence of transformation of austenite toma-rtensite, depending, of course, upon a given nickel and molybdenumcontent. To obtain optimum results when the molybdenum content is on thehigh side, to wit, 14.5% to 16%, the cobalt content should not exceedabout 22%. Further, provided that the molybdenum content is at least 11%and preferably at least 12%, the requirement that the sum of themolybdenum plus cobalt be at least 20% can be relaxed to the extent thatthe cobalt content can be lowered to 6%. In addition, it is preferredthat the elements nickel, molybdenum and c balt be correlated such thatthe sum of the nickel plus the molybdenum plus one-tenth of the cobaltis not less than 16 and not greater than 27 and most advantageously notless than about 20 and not greater than 26. This correlation greatlycontributes to achieving the formation of a satisfactory martensiticcondition upon cooling from hot working (or solution treating) Withoutthe necessity of using additional treatments, such as cold treating. Themaximum sum of the nickel plus molybdenum plus onetenth of the cobaltcan be as high as about 30 or even higher but, in this connection, acold treatment as by, for example, refrigeration and/ or cold working,may be necessary prior to aging to induce the desired degree oftransformation to martensite. The important or essential point is thatthe alloys be in the martensitic or substantially martensitic conditionprior to aging.

Titanium and/ or aluminum serve to provide good deoxidation andmalleabilization characteristics. Titanium, for example, serves to fixelements, such as oxygen, nitrogen and carbon. While the respectiveamounts of titanium or aluminum generally need not exceed about 1%, thetotal thereof not exceeding 1.5%, when molybdenum is present within thelow side of the molybdenum range, e.g. 7% to 10%, titanium and/ oraluminum in an amount of 1%, e.g., 1.5%, to about 3% markedly serves toenhance the strengthening characteristics (as shown hereinafter),particularly in the presence of nickel at the higher end of the nickelrange, e.g., 11% to 16% nickel.

While carbon can be present up to 0.3%, for good toughnesscharacteristics it should not exceed 0.1% except where unconventionalworking practices are employed, e.g., ausforming. For optimum results,carbon should not be present in amounts greater than 0.05%, e.g., notmore than about 0.03%. It should be mentioned that for applicationswhere carbides would be particularly useful, e.g., cutting edges, carboncontents up to 1% can be employed. Further, where good ductilitycharacteristics are of especial importance, manganese and silicon eachshould not be present in amounts above about 0.25% and preferably notabove 0.15%.

In addition to the foregoing and as referred to above herein, certaincompositional ranges of alloys afford special properties, e.g.,exceedingly high strengths and/or hardness, a high magnitude of strengthplus good tensile ductility, etc. Thus, for example, where a strengthlevel of about 425,000 p.s.i. or above would be of utmost importance, itis advantageous that the alloy be of the following composition: about 7%to 13% nickel, about 12% to 15% molybdenum, about 12% to 22% cobalt, upto 1% titanium, up to 1% aluminum, up to 0.1% carbon with the balanceessentially iron. Most advantageously, such alloys should contain 7% toabout 10.5% nickel, 12.5% to 14.5% molybdenum, about 14% to cobalt, upto 0.5 titanium, up to 0.5% aluminum, the sum of the titanium plusaluminum not exceeding 0.75%, up to 0.05% carbon and the balanceessentially iron. In this connection, the molybdenum content can belowered to about 10%, i.e., 10% to 12%, provided the cobalt content ispresent in amounts of to Where a good combination of strength (375,000p.s.i. to about 425,000 p.s.i.) and tensile ductility would be required,the alloy should contain about 11% to 16% nickel, about 7.5% to 12%molybdenum, about 10% to 18% cobalt, the sum of the molybdenum pluscobalt being at least 22% and the balance essentially iron.Advantageously for an optimum combination of strength and ductility, thealloy should contain 12.5% to 15.5% nickel, 8% to 10.5% molybdenum, 12%to 16% cobalt, the sum of the molybdenum plus cobalt being at least 22%,up to 0.05% carbon, up to 0.5% titanium, up to 0.5% aluminum, the totaltitanium plus aluminum not exceeding 0.75%, with the balance beingessentially iron. Should maximum hardness be the property of primaryinterest, the alloy should contain 5% to 10% nickel,

13% to 16% molybdenum and 16% to 30% cobalt. Another highly satisfactoryrange for exceptionally hard ferrous-base alloys is 6% to 9% nickel,13.5% to 15.5% molybdenum and 20% to 30% cobalt, the balance beingessentially iron.

In carrying the invention into practice, air or vacuum melting practicecan be utilized, preferably followed by consumable electrode melting foroptimum efifects. It is advantageous to utilize materials of good purityto thereby minimize the occurrence of inclusions, contaminants, etc. Inprocessing, the initially formed cast ingots should be thoroughlyhomogenized as, for example, by soaking, at a temperature of about 2200F. to about 2300" F. for about one hour per inch of cross section.Thereafter, the alloys are hot worked (as by forging, pressing, rolling,etc.) and, if desired, cold worked to desired shape. A plurality ofheating and hot working operations can be used and are advantageous toassure thorough homogenization of the cast structure through diffusionand to break up the cast structure. Hot working can be sati factorilycarried out over a temperature range of 2300 F. or 2200 F. down to 1400F., e.g., 2150 F. to 1500 F., with suitable finishing temperatures beingabout 2000 F. down to about 1500 F. Cooling from hot working ispreferably accomplished by air cooling although furnace cooling,quenching, etc., can be employed.

Subsequent to cooling from the hot Working temperature to efiect atransformation to the martensitic condition, the steels can be directlyaged (no other processing or heating step being necessary) by heating ata temperature of about 750 F. to 1100 F. for about hours to 0.1 hour,the longer aging periods being used in conjunction with the lower agingtemperatures. Aging at 950 F. to 900 F. for about one to four hours hasbeen found quite satisfactory. With aging times above about an hour orso, temperatures above about 1100 F. should not be used sincedeleterious austenite reversion can occur. On the other hand,temperatures appreciably below 750 F. are not recommended in view of thelong aging times required, e.g., more than 100 hours, to obtain maximumstrength and hardness. However, where especially hard surfaces,particularly in combination with softer cores, are required, the steelscan be heated at a temperature as high as 1400 F., e.g., about 1200 F.to 1375 F. and preferably at 1250 F. to 1350 F., for a period of time ofnot greater than about 30 minutes, e.g., up to 15 minutes, the longertime being associated with the lower temperature. A period of from a fewseconds, e.g., 15 seconds, up to five minutes is satisfactory for thetemperature range of 1250 F. to 1350 F.

Where desired or deemed advantageous, the steels can be subjected to asolution annealing treatment prior to aging. In this connection, thetemperature extends over a range of about 1400 F. to about 2200" F.;however, the temperature used in dependent upon the molybdenum contentto a considerable extent. Thus, in accordance herewith, when themolybdenum content is from 7% to about 8%, a solution treatmenttemperature (if employed) of at least about 1400 F. should be used. Withmolybdenum contents from above about 8% to about 10%, from above about10% to 12%, from above about 12% to 14% and above about 14%, solutiontreatment temperatures of at least about 1600 F., 1800 F., 1900 F., and2000 F., respectively, should be employed. With lower temperatures,there is the risk of finishing the steels cold such that best results,notably strength, are not obtained.

For the purpose of giving those skiled in the art a better understandingof the invention and/or a better appreciation of the advantages thereof,the following illustrative description and data are given.

In Table I a substantial number of alloy compositions are given togetherwith strength and hardness characteristics, the alloys beingillustrative of those which manifest exceptionally high strength andhardness. The alloying 8 p.s.i. for a specimen of Alloy No. 3 subjectedto Heat Treatment A. This further attribute of the invention, to wit,high ratios of yield to ultimate tensile strength, is of significantimportance since rare is the occasion that a constituents were melted ina vacuum induction furnace 5 designer is not restricted or limited tousing the yield and, after solidification, the cast ingots werehomogenized strength of a material (as opposed its higher ultimate(soaked) at about 2200 F. to 2300 F. The steels were tensile strength)as a basic criterion in selection of a then hot worked and thereaftermachined to specimens material for a given application. In accordancewith the of about 0.135 to 0.14 inch in diameter. The steels werepresent invention the ratio of yield strength to ultimate then heattreated at about 900 F. for about 4 hours 10 tensile strength isadvantageously at least 0.9 and higher, (Heat Treamtent A) or for fivehours (Heat Treatment e.g., 0.95 and above. It is Worthy of mention tosay that B) or at about 950 F. for about one hour (Heat Treatthe tensileductility (4 x diameter) of various of the ment C). None of the alloyswas given a solution treatalloys in Table I was exceptionally high forsuch strength ment subsequent to the hot working operation. Theultilevels, the highest, for those tested, being a tensile elonmatetensile strength (U.T.S.) is given in thousands of 15 gation of 4% forAlloy No. 2 (non-cold worked condipounds per square inch and thehardness is given in Rocktion, Heat Treatment C), and 2% for Alloy No.12. well C, R units. In addition to the constituents reported In TableII further data are given including strength in Table I, not more thanabout 0.03% carbon nor more (Y.S., 0.2% offset), tensile ductility (EL,percent) and than about 0.15% silicon plus manganese was added toreduction in area (R.A., percent) values, the data being the steels, thebalance otherwise being iron plus impuri- 20 illustrative of alloycompositions manifesting a good ties. combination of both strength andductility. In addition TABLE I Alloy Heat Ni, Mo, Co, Ti, Al, U.'I.S.,Hardness,

N 0. Treatment percent percent percent percent percent p.s.i. R c

A s 14 1s 0. 2 0. 2 506. 200

A 8 14 18 0. 2 N.A. 490,100 64. 5

o s 14 13 0. 2 N.A. 476,706

o s 14 1s 0. 2 N.A. 476, 500

A s 14 18 N.A. 0. 2 467, 800 65.

o s 14 1s N.A. 0. 2 468, 000

A s 14 1s N.A. 0. 2 461, 900 65 0 s 14 1s N.A. 0. 2 479, 560

1 Cold worked about before aging. 2 0.5% columbium added. 3 Difierentheat from Alloy N0. 1.

N .A.--Not added.

As is apparent from Table I, ultimate tensile strengths well above400,000 p.s.i. can be readily obtained in accordance with the invention.As reflected by Alloys Nos. 1 and 2, the half-million p.s.i. strengthbarrier was passed with the application of a nominal amount of coldworking prior to aging such alloys and, as a practical matter, wasreached by Alloy No. 3 without cold working. The hardness level for eachof the alloys exceeded R 60. The yield strengths of the alloys (notgiven) were also exceptionally high, being exceedingly close to thecorresponding ultimate tensile strengths. For example, the yieldstrength (0.2% offset) of Alloy No. '1 (non-cold worked condition) was473,800 p.s.i. and for Alloy No. 18 it was to Heat Treatments A and Cheretofore described, on occasion, other heat treatments were used asfollows: aging for about 96 hours at about 800 F. (Heat Treatment D);refrigerating before aging at 900 F. for about four hours (HeatTreatment E). The alloys were prepared following the procedure used inconnection with the alloys of Table I, except that the specimens wereabout 0.252 inch in diameter and in a few instances air melting practicewas used. In addition to the alloying constituents and amounts thereofset forth in Table II, none of the alloys contained more than about0.04% carbon nor more than about 0.15% of each of silicon and 441,000p.s.i. The highest yield strength was 486,700 manganese. A small amountof aluminum and titanium,

0.2% of each, was added to each melt, the balance of the alloys beingiron plus impurities.

10 about 10% or 11%, tensile strengths of about 425,000 p.s.i. andabove, e.g., 450,000 p.s.i., can be obtained pro- TABLE II Allo Heat N1,M0, Co, U.T.S., Y.S., EL, R.A.,

N0. Treatment percent percent percent p.s.i. p.s.i. percent percent A 1212 12 415, 000 402, 000 3 16 A 10 12 12 415, 000 404, 000 4 10 A 9 13 13411, 000 403, 000 3. 5 23 D 13 12 400, 800 388, 300 8 38. 5 A 13 10 12402, 400 394, 900 6 23 A 12 10 16 402, 000 390, 000 5 27 A 13 9 16 399,000 86, 000 5 23 A 12 10 14 394, 000 381, 000 4 24 A 13 9 14 393, 400380, 100 5 30 O 13 9 14 392, 600 384, 100 7 33 E 13 9 14 393, 100 383,100 6 24 E 14 8 16 383, 200 375, 200 8 28 A 14 8 16 384, 100 375, 000 525. 5 D 14 8 16 380, 300 371, 200 9 37. 5

*Air melted.

The data in Table II reflects that a markedly good combination ofstrength and tensile ductility can be obtained in accordance herewith.For example, at a yield strength of about 388,000 p.s.i., Alloy No. 26manifested an exceptionally high tensile ductility of about 8% togetherwith a reduction in area of about 38%. The data further illustrates thecloseness between the yield and ultimate tensile strengths, the ratiotherebetween being not less than 0.95% for any of Alloys Nos. 23 through33.

As has been indicated hereinbefore, when the molybdenum content of thealloys is maintained at about 10% or below, aluminum and/ or titaniummarkedly enhance the strength characteristic of the alloys. This isillustrated in Table III.

vided the sum of aluminum plus titanium is at least 1%. In this case,the alloys can contain 5% to 16.5% nickel, about 7% to 11% molybdenum,about 8% to about 30% cobalt, the sum of the molybdenum plus cobaltbeing at least 20%, at least one metal selected from the groupconsisting of up to 2.5% titanium and up to 2.5% aluminum, the sum ofthe titanium plus aluminum being at least 1% and not greater than 3%, upto 0.3% carbon, the balance being essentially iron. Advantageously suchalloys contain 7% to 15% nickel, about 7% to 10% molybdenum, about 10%to 25% cobalt, at least one metal selected from the group consisting ofup to 2.25% titanium and up to 2.25 aluminum, the sum of the titaniumplus aluminum being at least 1.5% and not greater than 2.5%, up

TAB LE III Alloy Heat i, Mo, C0, Ti, Al, U.T.S No. Treatment percentpercent percent percent percent p.s.i.

A 12 10 14 0. 2 0. 2 394, 000 A 12 10 16 0. 2 0. 2 402, 000 A 12 10 160. 2 1 430, 000 A 12 10 16 1 0. 2 445, 000 A 12 10 16 0. 8 0. 8 450, 000A 12 10 16 2 0. 2 463, 000

As can be seen from Table III, the increase in strength of Alloy No. 27over Alloy No. 29 is due to the increase in cobalt. Increasing thealuminum or titanium content of Alloy No. 27 from 0.2% to 1% as inAlloys Nos. 19 and 17, respectively, resulted in a marked increase instrength. The greatest increase occurred in respect of Alloy No. 9wherein the titanium content was 2%. Equal amounts of aluminum andtitanium, i.e., 0.8%, in Alloy No. 15 indicate that an excellentincrease in strength can be had over Alloy No. 27 which contained 0.2%of each of titanium and aluminum. The magnitude of this strikingimprovement does not follow With alloys containing 5 ment A.

TABLE IV Alloy Ni, Mo, 00, Ti, Al, Hardness,

N 0. Percent Percent Percent Percent Percent R0 9 5 5 0.2 32 2O 5 30 0.20 20 5 0.2 0 4 1O 0 0.2 27 20 10 10 0.2 0 19 10 15 0.2 0 18 1O 20 0.2 010 10 0.2 22 18 10 18 0.2 16 15 9 20 0.2 63.5 14 8 24 0.2 62.5 10 10 300.2 7 15 15 0.2 65 5 13 18 0.2 63

1 Air Melted.

l 4% Chromium Added.

much above 10% molybdenum, e.g., 12% or above, particularly in thepresence of nickel contents below 14%. Thus, where the molybdenumcontent does not exceed Each of Alloys Nos. 34 through 42 exhibitedextremely low hardness, hardness levels more than quite below thatcharacteristic of the alloys contemplated herein. Microstructure studiesof Alloys Nos. 34 through 40 (aged condition) revealed that only AlloyNo. 34 was martensitic, Alloys Nos. 35 through 40 being austenitic andAlloy No. 37 being ferritic. All the alloys within the invention weremartensitic and suflice to say the Rockwell hardnesses thereof were of amagnitude substantially higher than Alloys Nos. 34 to 42.

In addition to the fact that alloys within the invention afford a highdegree of strength and/ or hardness as well as being ductile, alloyscontemplated herein are also resistant to stress corrosion cracking. Thealloys are useful in the production of such items as bar, rod, plate,castings, wire, etc., and products made therefrom, including fasteners,e.g., bolts; In this connection, for optimum processing characteristics,at least titanium and/or aluminum should be used in an amount of atleast 0.05%, e.g., 0.1%. Desired shapes are best obtained prior toaging, i.e., in the hot worked or annealed condition since the alloysare comparatively soft and thus are more amenable to shaping operationssuch as cold working. Further, to minimize processing time, agingtemperatures from 850 F. to 950 F. are deemed the most satisfactory, theaging period not exceeding about ten hours.

As will be readily understood by those skilled in the art, the termsmartensite or substantially martensite include the decomposition and/ortransformation products of austenite obtained upon cooling from the hotworking operation (or, where used, a solution annealing treatment).These terms also include transformation products of austenite resultingfrom the application of a cold treatment, e.g., refrigeration at atemperature down to minus 300 F. and/ or cold working.

Although the present invention has been described in conjunction withpreferred embodiments, it is to be understood that modifications andvariations may be resorted to without departing from the spirit andscope of the invention, as those skilled in the art will readilyunderstand. Such modifications and variations are considered to bewithin the purview and scope of the invention and appended claims.

We claim:

1. A martensitic, iron-base alloy manifesting an exceptionally highcombination of strength and ductility in the aged condition, said alloyconsisting essentially of about 11% to about 16% nickel, about 7.5% toabout 12% molybdenum, about to about 18% cobalt, the sum of themolybdenum plus cobalt being at least 20%, up to 0.1% carbon, up to 1%titanium, up to 1% aluminum, the sum of the titanium plus aluminum notexceeding 1.5%, and the balance essentially iron.

2. The alloy as set forth in claim 1 wherein the sum of the molybdenumplus cobalt is at least 22%.

3. A martensitic, iron-base alloy manifesting an exceptionally highcombination of strength and ductility in the aged condition, said alloyconsisting essentially of 12.5% to 15.5% nickel, 8% to 10.5% molybdenum,12% to 16% cobalt, up to 0.05% carbon, up to 0.5% titanium, up to 0.5%aluminum, the sum of the titanium plus aluminum not exceeding 0.75%, andthe balance essentially iron.

4. The alloy as set forth in claim 3 wherein the sum of the molybdenumplus cobalt is at least 22% 5. A martensitic, ferrous-base alloycharacterized by a tensile strength of about 425,000 p.s.i. in the agedcondition and being of a composition within the following ranges: about7% to about 13% nickel, about 12% to about 15% molybdenum, about 12% toabout 22% cobalt, up to about 0.1% carbon, up to about 1% titanium, upto about 1% aluminum, the sum of the titanium plus aluminum notexceeding about 1.5%, and the balance essentially iron.

6. A martensitic, ferrous-base alloy characterized by a tensile strengthof above about 425,000 p.s.i. in the aged condition and being of acomposition within the following ranges: about 7.5% to about 10.5%nickel, about 12.5%

12 to about 14.5% molybdenum, about 14% to about 20% cobalt, up to about0.05% carbon, up to 0.5% titanium, up to 0.5% aluminum, the sum of thetitanium plus aluminum not exceeding 0.75%, and the balance essentiallyiron.

7. A martensitic, ferrous-base alloy characterized by a tensile strengthof above about 425,000 p.s.i. in the aged condition, said alloycontaining about 7% to 10% nickel, about 10% to 12% molybdenum, about25% to 30% cobalt, up to 0.1% carbon, up to 1% titanium, up to 1%aluminum, the sum of the titanium plus aluminum not exceeding 1.5%, andthe balance essentially iron.

8. A martensitic, iron-base alloy characterized by a hardness of atleast Rockwell C 60 in the aged condition and containing from 5% toabout 10% nickel, from 13% to 16% molybdenum, from 16% to 30% cobalt, upto 0.1% carbon, up to 1% titanium, up to 1% aluminum, the sum of thetitanium plus aluminum not exceeding 1.5 and the balance essentiallyiron.

9. A martensitic, iron-base alloy characterized by a hardness of atleast Rockwell C 60 in the aged condition and containing from 6% to 9%nickel, from 13.5% to 15.5% molybdenum, from 16% to 30% cobalt, up to0.05% carbon, up to 0.75% titanium, up to 0.75% aluminum, the sum of thetitanium plus aluminum not exceeding 1% and the balance essentiallyiron.

10. The alloy as set forth in claim 9 wherein the cobalt does not exceedabout 22%.

11. An iron-base alloy consisting essentially of from 5% to about 16.5%nickel, about 7% to about 16% molybdenum, about 8% to about 30% cobalt,the sum of the molybdenum plus cobalt being at least about 20%, up to2.5% titanium, up to 2.5 aluminum, the sum of the titanium plus aluminumnot exceeding about 3%, up to 1% carbon, up to 2% columbium, up to 4%tantalum, up to 0.1% boron, up to 0.25% zirconium, up to 8% chromium, upto 2% vanadium, up to 0.5% silicon, up to 0.5% manganese, up to 1%beryllium, up to 4% copper, up to 0.1% calcium, the total amount ofcolumbium, tantalum, boron, zirconium, chromium, vanadium, silicon,manganese, beryllium, copper and calcium being not more than 10%, andthe balance essentially iron.

12. The alloy as set forth in claim 11 wherein the molybdenum ispartially replaced by an equal atomic percentage of tungsten up to amaximum tungsten content of 8% such that the sum of the molybdenum plusone-half the tungsten plus the cobalt is at least 20%.

13. The alloy as set forth in claim 11 wherein the sum of the nickelplus molybdenum plus one-tenth of the cobalt does not exceed about 30%and is not less than about 16%.

14. The alloy as set forth in claim 11 where the carbon content does notexceed 0.3%.

15. The alloy as set forth in claim 14 wherein the cobalt content doesnot exceed about 22% and the sum of the nickel plus molybdenum plusone-tenth the cobalt does not exceed about 27%.

16. The alloy as set forth in claim 15 wherein the carbon, silicon andmanganese contents do not exceed 0.05%, 0.15% and 0.15%, respectively.

17. The alloy as set forth in claim 16 wherein the sum of the molybdenumplus cobalt is at least 22% and the sum of the nickel plus molybdenumplus one-tenth the cobalt does not exceed 26% and is not less than 20%.

18. A martensitic, iron-base alloy consisting essentially of from about7% to about 15% nickel, about 8% to about 15% molybdenum, about 10% toabout 25% cobalt ,the sum of the molybdenum plus cobalt being at least22%, up to 2.5% titanium, up to 2.5% aluminum, the sum of the titaniumplus aluminum not exceeding about 2.5%, up to 0.1% carbon, and thebalance essentially iron.

19. The alloy as set forth in claim 18 wherein the sum of the nickelplus molybdenum plus one-tenth the cobalt does not exceed 26% and is notless than about 20%.

20. The alloy as set forth in claim 19 wherein the cobalt content doesnot exceed about 22%.

21. The alloy as set forth in claim 20 wherein a total of not more than6% of the following elements are present: up to 1.5% columbium, up to 3%tantalum, up to 0.05% boron, up to chromium, up to 1.5% vanadium, up to0.15 zirconium, up to 0.25% silicon, up to 0.25% manganese, up to 0.5%beryllium, up to 2% copper and up to 0.1% calcium.

22. The alloy as set forth in claim 21 wherein the carbon, silicon andmanganese contents do not exceed 0.05%, 0.15% and 0.15%, respectively.

23. The alloy as set forth in claim 22 wherein the sum of the molybdenumplus cobalt is at least 23% and carbon is present in an amount up to0.03%.

24. The alloy as set forth in claim 22 wherein the molybdenum isrepla-ced by an equal atomic percentage of tungsten up to a maximumtungsten content of 4% such that the sum of the molybdenum plus one-halfthe tungsten plus the cobalt is at least 23% and the sum of the nickelplus molybdenum plus one-half the tungsten plus one-tenth the cobaltdoes not exceed 26% and is not less than about 20%.

25. A martensitic, iron-base alloy consisting essentially of from 5% to16.5% nickel, from 7% to 11% molybdenum, from 8% to 30% cobalt, the sumof the molybdenum plus cobalt being at least 20%, up to 2.5% titanium,up to 2.5 aluminum, the sum of the titanium plus aluminum being not lessthan 1% nor greater than 3%, up to 0.3% carbon, up to 0.5% silicon, upto 0.5 manganese, and the balance essentially iron.

26. The alloy as set forth in claim 25 wherein the sum of the nickelplus molybdenum plus one-tenth the cobalt does not exceed 27% and is notless than 16%.

27. A martensitic, iron-base alloy consisting essentially of from about7% to about 15% nickel, about 7% to 10% molybdenum, about 10% to 25%cobalt, the sum of the molybdenum plus cobalt being at least 22%, up to2.25% titanium, up to 2.25 aluminum, the sum of the titanium plusaluminum being not less than 1.5% nor greater than 2.5%, up to 0.1%carbon, up to 0.5% silicon, up to 0.5 manganese, and the balanceessentially iron.

28. An alloy as set forth in claim 27 wherein the sum of the nickel plusmolybdenum plus one-tenth the cobalt does not exceed about 26% and isnot less than 20%.

29. The alloy as set forth in claim 28 wherein the carbon, silicon andmanganese contents do not exceed 0.05%, 0.25 and 0.25 respectively.

30. The alloy as set forth in claim 29 wherein the carbon, silicon andmanganese contents do not exceed 0.03%, 0.15% and 0.15%, respectively.

31. A martensitic, iron-base alloy consisting essentially of from 5% to16.5% nickel, about 11% to 16% molybdenum, about 6% to 30% cobalt, up to0.3% carbon, up to 1% titanium, up to 1% aluminum, the sum of thetitanium plus aluminum not exceeding 1.5 and the balance essentiallyiron.

32. The alloy as set forth in claim 31 wherein molybdenum is present inan amount of from 12% to 15 the cobalt content does not exceed 22% andthe carbon content does not exceed 0.05%.

References Cited UNITED STATES PATENTS 3,093,519 6/1963 Decker et al.-123 X 3,154,412 10/1964 Kasak et a1. 75-126 3,166,406 1/ 1965 Floreenet a]. 75-124 3,243,285 3/ 1966 Fragetta et al. 75-123 3,251,683 5/1966Hammond 75-128 DAVID L. RECK, Primary Examiner.

P. WEINSTEIN, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE DECORRECTION Patent No.3,359,094 December 19, 1967 Clarence G. Bieber et a1.

It is certified that error appears in the above identified patent andthat said Letters Patent are hereby corrected as shown below:

Column 1, line 38, "eflorts" should read efforts Column 2, line 58 "as"should read As Column 4, lines 4 and 7, "01%", each occurrence, shouldread 0.1% Column 6, line 58, "in" should read is line 72, "skiled"should read skilled Column 7, line 11, "Treamtent" should read TreatmentColumn 9, line 19, "reflects" should read reflect line 25, "illustrates"should read illustrate Column 11, line 63, before "about" insert aboveSigned and sealed this 16th day of December 1969.

(SEAL) Attest:

Edward M. Fletcher, J1. WILLIAM E. SCHUYLER, JR.

Attesting Officer Commissioner of Patents

11. AN IRON-BASE ALLOY CONSISTING ESSENTIALLY OF FROM 5% TO ABOUT 16.5%NICKEL, ABOUT 7% TO ABOUT 16% MOLYBDENUM, ABOUT 8% TO ABOUT 60% COBALT,THE SUM OF THE MOLYBDENUM PLUS COBALT BEING AT LEAST ABOUT 20%, UP TO2.5% TITANIUM, UP TO 2.5% ALUMINU, THE SUM OF THE TITANIUM PLUS ALUMINUMNOT EXCEEDING ABOUT 3%, UP TO 1% CARBON, UP TO 2% COLUMBIUM, UP TO 4%TANTALUM, UP TO 0.1% BORON, UP TO 0.25% ZIRCONIUM, UP TO 8% CHROMIUM, UPTO 2% VANADIUM, UP TO 0.5% SILICON, UP TO 0.5% MANGANESE, UP TO 1%BERYLLIUM, UP TO 4% COPPER, UP TO 0.1% CALCIUM, THE TOTAL AMOUNT OFCLOUMBIUM, TANTALUM, BORON, ZIRCONIU, CHROMIUM, VANADIUM, SILICON,MANGANESE, BERYLLIUM, COPPER AND CALCIUM BEING NOT MORE THAN 10%, ANDTHE BALANCE ESSENTIALLY IRON.